In my copending patent application, "Color Monitoring System For Use In Creating Colored Displays" Ser. No. 951,444 filed Oct. 13, 1978, a system is described wherein a scanning densitometer head is moved over a color swatch bar to read selected ones of the color swatches and automatically determine the color that it is viewing and record the optical density thereof. In order for the scanning head to make a meaningful excursion, the color swatch bar must be carefully located so that the light beam from the scanning head strikes each color swatch as close to the center as possible. When the user is going to effect a scan, he places the copy with the color swatch bar under a bridge-like arrangement along which the scanning head is moved by a belt. Unless he can somehow line the center line (as considered lengthwise) of the color swatch bar with the center of the aperture in the base of the scanning head, then the scanning run of the head is likely to read misinformation. With the present device the wires lie in a plane which intersects a line defined by the center point of the aperture of the scanning head and which plane lies orthogonal to the plane in which the base of the head lies.